Method for producing good-flavor butter milk associated dairy product and dairy processed product

ABSTRACT

A process for preparing butter milk and/or butter serum, which comprises decreasing the dissolved oxygen concentration of at least one selected from the group consisting of milk, a milk product, butter milk and butter serum, followed by heating, and optionally fractionizing the heated product.

This application is a 371 of PCT/JP03/15811, filed Dec. 10, 2003.

FIELD OF THE INVENTION

This invention provides a production process capable of improvingflavor, physical properties and shelf life of butter milk-related dairyproducts and processed milk products, which have hardly been used asfood materials in Japan because, in spite of their excellentcharacteristics such as high nutritive values, various physiologicalfunctions and reinforcement of milk flavor of food, they undergooxidation mainly due to dissolved oxygen from the air which quicklygenerates unpleasant taste and smell, and also provides buttermilk-related dairy products, processed milk products and the like havinggood flavor which are obtained by this production process.

BACKGROUND ART

Both butter milk and butter serum are pale yellow liquids which aregenerated as by-products together with the butter and butter oil ofinterest in producing butter from cream prepared to a milk fat contentof from 30 to 40% in the former case, and in producing butter oil frombutter or high fat cream in the latter case, by a physical fractionationoperation such as centrifugation which makes use of the difference inspecific gravity or demulsification represented by churning effected bythe collision of milk fat globules. By further concentrating or drying(butter milk powder) these liquids, various types of butter milk-relateddairy products and processed milk products are produced. In Europe andAmerica, butter milk is also produced when fermented butter is produced,after fermenting cream by inoculating a lactic acid bacterium, and thisis generally called acidic butter milk. On the other hand, a product bya process without fermentation is called sweet butter milk. Objects ofthe present invention do not distinguish kinds of sweet and acidicbutter milks. Also, though butter milk and butter serum aredistinguished based on the difference of the dairy products used intheir production, basic differences are not found in terms of their milkcomponents, physical properties and the like, so that butter serum isregarded in the present invention as a part of butter milk in a broadsense (hereinafter, the term butter milk sometimes includes butterserum).

It is said that butter milk contains lipids, proteins, carbohydrates,minerals, vitamins and the like similar to the case of milk, and itsnutritive value per solid matter is almost the same as that of milk.However, as can be understood from its production method, it ischaracterized by the presence of a large amount of milk fat globulemembrane substance constituting the interface of milk fat globules, andit is known that milk fat globule membrane substance-characteristiclipoproteins and glycoproteins are present as the membrane proteins, inaddition to casein, α-lactalbumin and β-lactoglobulin. Also, it is saidthat it contains a large amount of phospholipids which are generallyreferred to as lecithin, in addition to the general triglycerides(neutral lipids) as the membrane constituting lipids, occupying from 29to 36% of the milk fat globule membrane substance. The mainphospholipids are phosphatidylcholine, sphingomyelin andphosphatidylethanolamine, and when compared with lecithin derived from aplant such as soybean, the milk lecithin is particularly characterizedby the presence of sphingomyelin in a considerably large amount ofapproximately 18%, which is close to the composition of human milklecithin, so that its nutritional application value is considered to bemarkedly high.

In addition, since butter milk richly contains aromatic components whichare characteristic to butter, it is a desirable material from theviewpoint of flavor, too. The aromatic components are composed ofketones, fatty acids, lactones and the like, and are particularlycharacterized in that ketones are contained in an overwhelmingly largeamount of 78% even when compared with other dairy products.

On the other hand, it is said that butter milk is also effective for thetreatment of acute hepatitis and gastric mucosal sepsis and theprevention of diarrhea of babies. It is also considered that it has ablood pressure reducing activity and serum cholesterol reducingactivity.

Thus, in spite of the excellent characteristics such as high nutritivevalue, various physiological functions and reinforcement of milk flavorof food, the application of butter milk as a food material has hardlybeen developed, because it is apt to undergo oxidation due to thedissolved oxygen from the air which quickly generates unpleasant tasteand smell. Currently in Japan, butter milk generated during theproduction of butter is mostly discarded without any application, whichmust be regarded as a serious loss of a food resource.

Two methods are known for effecting long-term storage of butter milk,namely (1) a method in which the number of microorganisms in thegenerated butter milk is controlled to a predetermined level or less bya batch or plate heating treatment, and the resulting butter milk isconcentrated under a reduced pressure using an evaporator, subjected tofinal sterilization and then frozen to obtain a butter milk concentrateand (2) a method in which the butter milk concentrate obtained in (1) byconcentrating under a reduced pressure using an evaporator is made intopowder using a spray drying apparatus (dryer). Since butter milk ishighly concentrated in either method, the produced butter milk-relateddiary products are apt to undergo oxidation by oxygen in the air,considerably strongly, so that in order to avoid this, each product isgenerally packed in a can or an aluminum foil-lined polyethyleneprocessed paper container and stored in a cool and dark place. However,even when it is stored in a cool and dark place using these sealedcontainers, foul taste and smell due to generation of oxidized productsbecomes strong within approximately 1 to 3 months, or within about 1week after opening of the container, so that the shelf life isconsiderably poor and its application value as a food processingmaterial (e.g., “Nyuseihin Kogyo (Dairy Products Industry), the secondvolume”, published on Feb. 25, 1972, pp. 223-224, edited by TomokichiTsugo, published by Chikyu Shuppan) is low.

In addition, by taking note of the fact that butter milk contains milkfat globule membrane substance in a large amount, it has been reportedon a method in which the fat globule membrane substance is fractionatedand purified from butter milk and used as a food flavor improving agent(JP-A-7-236451) and a method in which the milk fat globules are removedfrom butter milk by centrifugation and then the ultrafiltrationvitrification liquid is used as a food flavor improving agent (JapanesePatent No. 3004912). However, each of these methods is a techniquerelated to the fractionation and purification of the milk fat globulemembrane substance in butter milk, and it is evident that this techniqueis basically different from the technique of the present invention whichis intended to prevent generation of oxidized smell caused by undergoinginfluence of the oxidation based on the dissolution of air oxygen inbutter milk, thereby keeping and improving the milky flavor inherent tothe butter milk. In addition, although the degree of flavor may vary, aswill be described later, generation of oxidized smell of the flavorimproving agents obtained by these techniques cannot be avoided, so longas a heat treatment is carried out in the presence of unsaturated fattyacids and milk proteins.

In the field of dairy industry, a process has been reported in which adrink having a flavor close to crude milk or unheated solution of milkis produced by carrying out heat treatment of milk or a milk-containingunheated solution after reducing dissolved oxygen in the liquid prior totheir heat treatment (JP-A-10-295341), and also a sterilization methodwhich does not generate heated smell, as a method for sterilizing milkand the like by replacing dissolved oxygen therein with nitrogen gas, inwhich sterilization is carried out after reducing amount of dissolvedoxygen in milk and the like by replacing dissolved oxygen by nitrogengas, effected by the combined use of a means wherein nitrogen gas isdirectly mixed and dispersed in milk and the like and a means whereinmilk and the like which are not contaminated with nitrogen gas aresprayed from the upper side through a nozzle to nitrogen gas-mixed anddispersed milk and the like stored in a nitrogen gas-replaced tank undera nitrogen gas atmosphere (Japanese Patent No. 3091752). However, theobjects of these methods for keeping and improving flavor are milks ofcow, horse, goat, sheep, water buffalo, human and the like mammals, andproducts containing these milks, such as milk based drinks, processedmilk, fortified or separated milk beverages, reduced milk, fermentedmilk, lactic acid bacteria beverage, fresh cream, fruit juice drink andthe like, but nothing is reported therein about the butter milk whichundergoes influence of the oxidation by oxygen in the air considerablystrongly as described in the foregoing.

DISCLOSURE OF THE INVENTION

An object of the present invention is to extremely extend the use ofapplication of butter milk-related dairy products and processed milkproducts in the food industry, by preventing generation of oxidizedsmell from these butter milk-related dairy products and processed milkproducts caused by the influence of oxidation based on the dissolutionof oxygen in the air, and thereby keeping and improving the milky flavorinherent to the butter milk, and also to overcome a technical problemfor total recovery of butter milk which previously had to be discarded,and thereby to achieve the effective utilization of food resources orthe reduction of risk of environmental pollution caused by theabandonment of food resources.

The present invention has been made with the aim of achieving the aboveobject, and inventors of the present invention have found as a result ofinvestigations from various angles that butter milk and/or butter serumwhich hardly generates oxidized flavor, and when it is drunk,characteristic to crude milk, palatable, having refreshing after-tasteand completely lacking unpleasant or foul taste and smell can beobtained by employing a method in which, during a process offractionating and preparing a partial or entire amount of butter milkand/or butter serum from milk and/or a dairy product, when applying aheat treatment to solution of milk and/or a diary product before thefractionation and preparation (in general, cream is used at the time ofproducing butter milk, and heating-dissolved butter at the time ofproducing butter serum), and/or butter milk and/or butter serum afterthe fractionation and preparation, which is carried out for the purposeof sterilizing these solutions and/or keeping and improving flavorthereof and/or preventing deterioration of their physical properties,dissolved oxygen concentration in the solution is reduced in advance (to8 ppm or less, preferably 5 ppm or less, more preferably 2 ppm or less)by injection of an inert gas or the like.

Also, a concentrated preparation obtained by concentratingdeoxidation-treated butter milk and/or butter serum under a reducedpressure using an evaporator and a powder obtained by drying anddisintegrating this using a dryer can also be made into products whichhardly generate oxidized smell, have good taste and refreshingafter-taste and completely lack in foul taste and smell in comparisonwith deoxidation-untreated concentrate and powder.

In addition, when production of new dairy products and processed milkproducts was carried out for the purpose of improving flavor by partialaddition of these butter milk-related dairy products to other milksand/or dairy products, the butter milk-inherent oxidized smell washardly felt and it was able to obtain products having stronger milkyflavor than usual diary products.

When application of the butter milk-related diary products and processedmilk products obtained in this manner by a deoxidation operation to foodand drink was verified, the finally obtained food and drink hardlygenerated the butter milk-inherent oxidized smell, and showed strongmilky flavor, good taste and refreshing after-taste, so that it was ableto verify the usefulness of the present invention.

The present invention relates to the following (1) to (10).

-   (1) A process for preparing butter milk and/or butter serum, which    comprises decreasing the dissolved oxygen concentration of at least    one selected from the group consisting of milk, a milk product,    butter milk and butter serum, followed by heating, and optionally    fractionizing the heated product.-   (2) The process according to (1), wherein the dissolved oxygen    concentration is decreased by addition of inactive gas.-   (3) The process according to (2), wherein the inactive gas is    nitrogen gas.-   (4) The process according to any one of (1) to (3), wherein the    dissolved oxygen concentration is 8 ppm or less.-   (5) The process according to any one of (1) to (4), wherein the    dissolved oxygen concentration is 5 ppm or less.-   (6) The process according to any one of (1) to (5), wherein the    dissolved oxygen concentration is 2 ppm or less.-   (7) A process for preparing a butter milk-related dairy product    and/or processed milk product, which comprises subjecting the butter    milk and/or butter serum prepared by the process according to any    one of (1) to (6) to at least one processing selected from the group    consisting of concentration, drying, fractionation, purification,    deodorizing, decoloring and addition of an additive.-   (8) A process for preparing a milk product or processed milk    product, which comprises adding at least one selected from the group    consisting of the butter milk, the butter serum, the milk product    and the processed milk product prepared by the process according to    any one of (1) to (7) to another milk and/or milk product.-   (9) A process for preparing food or drink, which comprises using, as    an addition material, at least one selected from the group    consisting of the butter milk, the butter serum, the milk product    and the processed milk product prepared by the process according to    any one of (1) to (8).-   (10) Butter milk, butter serum, a milk product, a processed milk    product, food or drink, prepared by the process according to any one    of (1) to (9).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a result of sensory evaluation of a buttercream after re-heat sterilization of a butter milk produced from a creamafter heat-sterilizing the cream under the condition of reducingdissolved oxygen to 8, 5 or 2 ppm.

FIG. 2 is a graph showing a result of the measurement of the —SH groupcontent in the above butter milk by a calorimetric determination (432nm).

FIG. 3 is a graph showing a result of the measurement of DMS, DMDS andDMTS in the above butter milk.

FIG. 4 is a graph showing a result of sensory evaluation of respectivebutter milks after heat sterilization of the butter milk obtained afterheat-sterilizing them under the condition of reducing dissolved oxygento 8, 5 or 2 ppm.

FIG. 5 is a graph showing a result of sensory evaluation of a reducedmilk to which a butter milk concentrate (nitrogen-sealed heatsterilization or nitrogen-unsealed heat sterilization) was added or notadded.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in the following in detail.

According to the present invention, the milk to be used as the origin ofbutter milk and/or butter serum is not particularly limited, so long asit is a mammalian milk, and examples include cow milk, goat milk, sheepmilk, water buffalo milk, sow milk, human milk and the like.

The milk and/or diary products to be used in producing butter milkand/or butter serum include crude milk, milk, special milk, partiallydefatted milk, whole milk powder, concentrated milk, evaporated milk,cream, butter and the like. Among these, cream and butter are generallyused industrially in view of the yield and productivity, so that exampleof the use of cream and butter is described in the following. However,the present invention does not exclude the use of milks and/or dairyproducts other than the cream and butter.

In general, a cream adjusted to a milk fat content of from 30 to 40% isheated by a plate heat exchanger under a sterilization condition of from85 to 95° C., and then cooled down to about 5° C. and subjected to agingin a storing liquid tank. Next, butter and butter milk are obtained bycarrying out churning (an operation in which milk fat globule membranesubstance is freed into water phase and butter particles are formed, bydestroying the interface structure of milk fat globule through thecollision of milk fat globules) at a temperature of from 7 to 13° C.using a batch type butter churn, continuous butter churn or the like.The thus obtained butter milk is again sterilized and transferred forconcentration under a reduced pressure using an evaporator. It wasconsidered that since the butter milk is subjected to heat treatment atleast twice before and after its separation in this manner, the heatedsmell is generated by the rapidly progressing oxidation reaction due tooxygen in the air dissolving in the butter milk.

It is a well known fact that milk components including butter milk causedenaturation of milk proteins by heating and thereby generate heatrelated unpleasant smell components represented by sulfur compounds suchas hydrogen sulfide, dimethyl sulfide (to be referred to as DMShereinafter), dimethyl disulfide (to be referred to as DMDShereinafter), dimethyl trisulfide (to be referred to as DMTShereinafter) and the like. That is, milk proteins (particularly wheyproteins represented by β-lactoglobulin) undergo thermal denaturation byheating, and disulfide bonds in sulfur-containing amino acid residues inpolypeptide chains are cleaved to expose —SH groups. On the other hand,the dissolved oxygen reacts with unsaturated fatty acids to formradicalized lipid peroxides. The radicalized lipid peroxides are said toreact with the —SH groups in the polypeptide chains of milk proteins toform various sulfur oxides which are detected as the heat relatedunpleasant smell components.

The lipids contained in milk (milk fats) are generally from 3.5 to 4.0%,and the constituting fatty acids broadly vary from butyric acid(C_(4:0)) to linolenic acid (C_(18:3)). Among these, it is consideredthat unsaturated fatty acids are particularly richly contained in themilk fat globule membrane substance in butter milk, and it is consideredthat the constituting neutral lipids and phospholipids contain from 2 to4% of palmitoleic acid, from 11 to 36% of oleic acid and from 2 to 11%of linoleic acid as unsaturated fatty acids, so that among the milkcomponents, they are particularly apt to be influenced by oxidation dueto dissolved oxygen.

Accordingly, taking into consideration that this rapid progress in theoxidation by oxygen in the air becomes a cause of the generation ofheated smell, an investigation was carried out on the process forreducing dissolved oxygen in a material cream by a deoxidation operationbefore the preparation of butter milk. As typical methods, two methods,namely ultrasonic treatment of the cream and replacement of theatmosphere in the cream by its sealing with an inert gas (nitrogen,argon or the like), were considered. As a result, the ultrasonictreatment could not withstand industrial production, because theinterface structure of milk fat globules in the cream was destroyedbefore heating sterilization, thereby causing changes in physicalproperties such as the viscosity increase and aggregation, while thesealing of an inert gas in the cream did not show particular changes inthe physical properties and changes in the physical properties were notobserved also by the subsequent heat sterilization. Therefore, it isconsidered that the latter method is a deoxidation operation most suitedfor the present invention.

In the case that an inert gas (hereinafter, the present invention isdescribed using nitrogen gas as a typical example) is sealed, it isdesirable that the sealing is carried out in a cream-stored tank and/orin lines reaching to a heating machine and at a liquid temperature of90° C. or less, preferably from 80 to 85° C. or less. However, sincedegassing of the sealed nitrogen gas becomes difficult in the case of acream of 30° C. or less, it is most suitable to carry out it inaccordance with the usual butter milk production method, by settingtemperature of the cream to from 30 to 40° C.

In general, concentration of dissolved oxygen in cream before thedeoxidation treatment is approximately from 10 to 15 ppm. When dissolvedoxygen concentration in the cream is reduced to 8 ppm or less byapplying the aforementioned deoxidation operation, and butter milk isprepared after carrying out its heat sterilization at 85 to 95° C.,oxidized smell of the product becomes weak, and the crude milk-specificgood taste and refreshing after-taste are expressed when compared withthe usual deoxidation-untreated butter milk. Particularly, this tendencybecomes significant when the dissolved oxygen concentration is reducedto 5 ppm or less, and the oxidized smell becomes hardly recognizablewhen reduced to 2 ppm or less.

On the other hand, when a butter milk fractionated without carrying outthe deoxidation treatment of cream after its heat sterilization at 85 to95° C., or directly without carrying out heat sterilization, wassubjected to the deoxidation operation by nitrogen gas sealing and tothe subsequent final heating at a temperature of from 85 to 130° C., theoxidized smell became weak and the crude milk-specific good taste andrefreshing after-taste were expressed when dissolved oxygenconcentration in the butter milk was reduced to 8 ppm or less.Particularly, this tendency became strong when the dissolved oxygenconcentration was reduced to 5 ppm or less, and the oxidized smellbecame hardly recognizable when reduced to 2 ppm or less. However, itspredominance in terms of flavor became slightly weak in comparison witha case when the cream as the starting material of butter milk wassubjected to the deoxidation operation.

In both cases, the minimum dissolved oxygen concentration in the creamis not particularly limited, and it is 0 ppm or more.

With regard to a nitrogen substitution apparatus for industriallycarrying out the deoxidation operation, it has been invented byinventors of the present invention (aforementioned Japanese Patent No.3091752) and put into practical use. Accordingly, the present inventionis a technique which can be carried out at once and is markedlyprofitable for the food industry.

In the case that concentration of the butter milk and/or butter serumobtained by the present invention is carried out for the purpose ofincreasing the solid content, a method such as concentration under areduced pressure by an evaporator such as a triple efficiencyconcentrator, or freeze concentration by a Glenco typefreeze-concentrator or the like, is employed. In the case of theconcentration under a reduced pressure by an evaporator, it is possibleto concentrate to a solid content of about 40% similar to the case ofthe usual butter milk concentrate employing no deoxidation operation.Also, it is possible to obtain a butter milk powder from this buttermilk concentrate in the usual way by heating it at 60 to 70° C. and thendrying it with hot air of from 130 to 200° C. using a dryer. The buttermilk concentrate and buttermilk powder obtained in this manner haveexcellent flavor, hardly generating oxidized smell, having good tasteand refreshing after-taste and lacking in unpleasant or foul taste andsmell, in comparison with deoxidation-untreated concentrate and powder.In addition, the obtained butter milk-related dairy products showexcellent shelf life in sealed containers.

These butter milk-related dairy products are directly used as foodmaterials in many cases. However, there are cases in which useful foodprocessing materials are produced from them by carrying out processingsuch as fractionation, purification, deodorization, decolorization,addition of additives and the like. An example is purification of milkfat globule membrane substance-derived lecithin richly contained inbutter milk. In this case, crude lecithin is prepared from butter milkby aqueous alcohol extraction and subsequent acetone extraction, andthen purified lecithin is obtained through the steps of water washing,sterilization and drying, and this process has been put into practicaluse. In this connection, when a deoxidation-treated butter milk is used,generation of an oxidized smell, called lecithin smell, is inhibited sothat excellent flavor is obtained.

The butter milk-related diary products and processed milk products thusdescribed in the foregoing have large effect to add milky flavor to foodand drink. They are broadly used in such applications as milk beverage,soft drink, fresh cream, compound cream, fermented milk, lactic acidbacteria beverage, fermented cream, dessert, ice cream, cheese, butter,margarine, bread, side dishes and the like, and the present inventioncan be applied to all food and drink.

EXAMPLES

The present invention is described in the following with examples, butthe present invention is not limited thereto.

Example 1

Into a tank, 2,000 kg of raw milk (milk fat content 3.8%, fat-free milksolid content 8.6%) was poured and heated up to 45° C., and then 180 kgof fresh cream having a milk fat content of 40% and a fat-free milksolid content of 5.4% was separated by centrifugation using a creamseparator and immediately cooled down to 5° C. with chilled water.

After 35 kg of the fresh cream was taken out and adjusted to itstemperature to 40° C., a heat sterilization was carried out at 95° C.for 15 seconds using an UHT/HTST dual purpose small plate typesterilization testing machine (flow rate 150 L/hr; manufactured by IwaiKikai), directly without sealing nitrogen gas, and then cooled down to5° C. The thus obtained cream weight was 20 kg (control cream).

After 35 kg of the fresh cream was taken out and adjusted to itstemperature to 40° C., nitrogen gas was sealed therein in such an amountthat dissolved oxygen became 8, 4 or 2 ppm. After allowing it to standas such for about 10 minutes and confirming that degassing wascompleted, its heat sterilization was carried out at 95° C. for 15seconds using the plate type sterilization testing machine and thencooled to 5° C. The thus obtained cream weight was 20 kg (samples 1, 2and 3). In this case, the dissolved oxygen concentration was measuredusing a dissolved oxygen meter (Type DO-21P; manufactured. by ToaElectronics).

Each of the control cream and samples 1, 2 and 3 was adjusted to itstemperature to 10° C. and then put into a batch type churn to carry outformation of butter particles by churning. The operation time was around45 minutes, and the thus obtained butter milk weight was about 10 kg andits milk fat content and fat-free milk solid content were 0.7% and 8.9%,respectively. These butter milk samples were subjected to heatsterilization at 95° C. for 15 seconds and then cooled down to 5° C.

These samples were subjected to the following tests.

By using the butter milk obtained from the control cream as a control,sensory evaluation of each of the thus obtained butter milk samples wascarried out by paired difference test using a panel of 30 professionalswho had a training for discriminating five tastes (sweetness, sourness,saltiness, bitterness and umami). Also, strength of oxidized smell ofeach butter milk sample was evaluated by scoring method by a panel of 5professionals. These results are shown in FIG. 1 and Table 1.

TABLE 1 Control butter Sample 1 Sample 2 Sample 3 milk (8 ppm) (5 ppm)(2 ppm) Heat oxidized 4.8 3.0 1.8 1.2 smell Evaluation points; 5: verystrong, 4: strong, 3: slightly strong, 2: slight sensation, 1: nosensation

At the same time, physical and chemical analysis of each butter milksample was carried out.

The —SH group content was measured by a calorimetric determination inaccordance with the method of M. Moka, E. M. Mikolajcik and I. A. Gould(J. Dai. Sci., 51, 2, 217-219 (1968)).

DMS, DMDS and DMTS were measured using a GC/MS (gas chromatograph massspectrometry) (HP6890 SERIES PLUS/HP5793 MSD; manufactured. by HitachiLtd.) by an HS/TCT (head space/thermal-desorption cold trapinjection)method.

Results of the analysis are shown in FIGS. 2 and 3.

As is apparent from the results shown in FIG. 1 and Table 1, as thedissolved oxygen in the cream was reduced, oxidized smell of butter milkbecame sensorially undistinguishable and, at the same time, expressionof the raw milk-inherent sensory characteristics such as good taste,freshness, good throat-passing feeling, good after-taste and the likealso became strong, so that the product became generally delicious inall these respects. This tendency became significantly distinguishableas the dissolved oxygen concentration became 5 ppm or less, and theoxidized smell was improved to a completely unfeeling level at 2 ppm.

Results of the physical and chemical analysis supported the abovesensory evaluation results. That is, as the dissolved oxygen in thecream was reduced by nitrogen sealing, formation of radicalized lipidperoxides was inhibited and a large number of unreacted —SH groupsremained as the result (FIG. 2). In addition, amounts of the sulfurcompounds (DMS, DMDS and DMTS) as the final products were also reducedat the same time, thus confirming that the heating smell components werereduced (FIG. 3).

Example 2

Fresh cream was obtained in 300 kg by carrying out a heat sterilizationat 95° C. for 15 seconds without sealing nitrogen gas in accordance withthe method shown in Example 1. Next, 150 kg of butter milk was obtainedusing a batch type churn without carrying out nitrogen gas sealing. Thecomposition was the same as in Example 1.

After 35 kg of the thus obtained butter milk was subjected to a heatsterilization at 95° C. for 15 seconds using the plate typesterilization testing machine at its temperature of 10° C. withoutsealing nitrogen gas, it was cooled to 5° C. The thus obtained buttermilk weight was 20 kg (control).

In the same manner, 35 kg of the butter milk was taken out and at itstemperature of 10° C., nitrogen gas was sealed in such an amount thatdissolved oxygen became 8, 4 or 2 ppm. The mixture was immediatelysubjected to a heat sterilization at 95° C. for 15 seconds using theplate type sterilization testing machine and then cooled to 5° C. Thethus obtained butter milk weight was 20 kg (samples 4, 5 and 6).

In the same manner as in Example 1, by using the nitrogen gas-unsealedbutter milk as a control, sensory evaluation of each of the thusobtained butter milk samples was carried out by paired difference testusing a panel of 30 professionals. Also, strength of oxidized smell ofeach butter milk sample was evaluated by scoring method by a panel of 5professionals. These results are shown in FIG. 4 and Table 2.

TABLE 2 Control butter Sample 4 Sample 5 Sample 6 milk (8 ppm) (5 ppm)(2 ppm) Heat oxidized 5.0 3.2 2.2 1.4 smell Evaluation points; 5: verystrong, 4: strong, 3: slightly strong, 2: slight sensation, 1: nosensation

As is apparent from the results shown in FIG. 4 and Table 2, as thedissolved oxygen in the butter milk was reduced, oxidized smell of thebutter milk became sensorially undistinguishable and, and at the sametime, expression of the raw milk-inherent sensory characteristics suchas good taste, freshness, good throat-passing feeling, good after-tasteand the like also became strong, so that the product became generallydelicious in all these respects. This tendency became distinguishable ata dissolved oxygen concentration of 5 ppm or less, and the oxidizedsmell was improved to a hardly detectable level at 2 ppm. However, thethus obtained butter milk generated a strong oxidized smell thoughslightly, in comparison with its counterpart prepared in Example 1, sothat the deoxidation operation by nitrogen sealing was more effectivewhen carried out at an initial stage of the production process.

Example 3

Investigation was made on the addition of the present invention to foodand drink. Each 250 g of a butter milk prepared from a fresh cream, inwhich nitrogen gas was not sealed or dissolved oxygen was reduced to 2ppm, was put into a vacuum evaporator and concentrated until its solidmatter increased four times. Next, 20 kg of the reduced milk (milk fatcontent 3.5%, fat-free milk solid content 8.3%) shown in Table 3containing 0.3% of these butter milk concentrates was prepared. Thereduced milk was emulsified using a homogenizer under a homogeneouspressure of 150 kg/cm², subjected to a heat sterilization at 130° C. for2 seconds using the plate type sterilization testing machine and thenimmediately cooled down to 5° C. or less, thereby obtaining respectivesamples.

TABLE 3 Nitrogen Nitrogen Reduced milk Control unsealed sealed (2 ppm)Salt-free butter 4.1 4.1 4.1 Skim milk powder 8.5 8.5 8.5 Four timesconcentrated 0.3 butter milk Four times concentrated 0.3 butter milk (2ppm) Raw water 87.4 87.1 87.1 Total 100.0 100.0 100.0

By using the butter milk with no additives made from reduced milk as acontrol, sensory evaluation of each of the thus obtained reduced milksamples was carried out by paired difference test using a panel of 30professionals. Also, strength of oxidized smell of each sample wasevaluated by scoring method by a panel of 5 professionals. These resultsare shown in FIG. 5 and Table 4.

TABLE 4 Nitrogen Nitrogen Control unsealed sealed (2 ppm) Heat oxidized1.0 2.4 1.2 smell Evaluation points; 5: very strong, 4: strong, 3:slightly strong, 2: slight sensation, 1: no sensation

As is apparent from the results shown in FIG. 5 and Table 4, it waspointed out that the milk to which the nitrogen-unsealed butter milkconcentrate was added increased a fatty taste but generated a certainfoul odor, so that butter milk concentrate was not necessarily evaluatedas a flavor improving agent, but in the case of the butter milkconcentrate whose dissolved oxygen was reduced to 2 ppm by carrying outnitrogen sealing, the raw milk-inherent sensory characteristics such asgood taste, freshness, good throat-passing feeling, good after-taste andthe like were strongly expressed in the milk too, so that the productwas felt generally delicious in all these respects. Thus, it wasconfirmed that the oxidized smell generation-inhibitory effect and milkyflavor improvement can be maintained by the present invention in thecase of batter milk-related diary products, too.

INDUSTRIAL APPLICABILITY

According to the present invention, the milky flavor originallypossessed by butter milk can be maintained and improved through theprevention of oxidized smell which is generated from batter milk-relateddiary products and processed milk products during their production byundergoing influence of oxidation based on the dissolution of oxygen inthe air. Although the use of application of these butter milk-relateddiary products and processed milk products in the food industry wasstrictly restricted in so far, by the present invention, the extremeexpansion of their use and the recycle of the entire amount of buttermilk which had to be discarded in so far are possible, and therefore thereduction of risk of causing environmental pollution by the disuse canbe achieved.

1. A process for preparing butter milk and/or butter serum, whichcomprises: subjecting raw cream to a first heat treatment at 85° C. to95° C., preparing butter milk and/or butter serum by subjecting the rawcream to churning, and subjecting the butter milk and/or butter serum toa second heat treatment at 85° C. to 130° C., wherein a dissolved oxygenconcentration of the raw cream is decreased to 8 ppm or less by additionof an inactive gas before the first heat treatment to the raw cream,and/or a dissolved oxygen concentration of the butter milk and/or butterserum is decreased to 8 ppm or less by addition of an inactive gasbefore the second heat treatment to the butter milk and/or butter serum.2. The process according to claim 1, wherein the addition of inactivegas is not conducted before the first heat treatment.
 3. The processaccording to claim 2, wherein the addition of inactive gas is notconducted before the second heat treatment.
 4. The process according toclaim 1, wherein the dissolved oxygen concentration of the raw creamand/or butter milk and/or butter serum is decreased to 2 to 8 ppm by theaddition of the inactive gas.
 5. The process according to claim 1,wherein the dissolved oxygen concentration of the raw cream and/orbutter milk and/or butter serum is decreased to 5 to 8 ppm by theaddition of the inactive gas.
 6. A process for preparing a buttermilk-related dairy product and/or processed milk product, whichcomprises subjecting the butter milk and/or butter serum prepared by theprocess according to claim 1 to at least one processing selected fromthe group consisting of concentration, drying, fractionation,purification, deodorizing, decoloring and addition of an additive.
 7. Aprocess for preparing a milk product or processed milk product, whichcomprises adding at least one selected from the group consisting of thebutter milk and butter serum prepared by the process according to anyone of claims 1 to 3 to another milk and/or milk product.
 8. A processfor preparing food or drink, which comprises using, as an additionmaterial, at least one selected from the group consisting of the buttermilk and butter serum prepared by the process according to any one ofclaims 1 to 3.